This invention relates to a remote control arrangement for use with communication apparatus. The invention relates more particularly to an improved remote control which utilizes a communication channel of the apparatus and which provides a control signal having a frequency lying within an information frequency band of the apparatus.
In various communication systems such as radio frequency broadcast and point to point communication systems, long line communication systems, etc., it is desirable not only to provide communication of intelligence between remotely located stations of the system but also, in some instances, to utilize a channel of the communication system for effecting the remote control of a function at one of the stations. The remotely controlled function may comprise, for example, the activation of a speaker for audible reproduction of audio intelligence, the activation of other circuit means, or the control of some element such as a fluid valve, a signal, a horn, or the like. From the viewpoint of simplicity and economy in the fabrication of the communication system, it is desirable to employ for the purposes of remote control the same band of frequencies in which the intelligence being communicated lies. In one form of communication system with which the present invention is particularly useful, a radio frequency carrier signal is modulated by intelligence occurring in the audio frequency band. The modulated carrier signal is broadcast and received by a remotely located receiver which tunes and amplifies the carrier signal; detects the audio modulation components; and audibly reproduces the intelligence. Transceiving apparatus employed in this system is experiencing continuously expanded use in the United States in a band of frequencies known as the citizens band and which presently is located around the 27 MHz radio frequency range.
When providing remote control for causing a particular reaction at the receiver, the receiving unit generally remains energized in order to provide active circuits which are responsive to a received signal. However, a background noise or hiss coupled with relatively heavy and continuous third party transmissions over the same communication channel produces a continuous audible transducer output. A continuous transducer audio output in the absence of intelligence directed to a particular receiving unit becomes annoying and reduces the responsiveness of an individual who is monitoring the particular receiving unit.
It has been found beneficial to eliminate the continuous audible background noise and reproduction of transmissions between other parties by providing a circuit arrangement which deactivates the audio transducer but which remains responsive to communications directed to the particular received for reactivating the transducer. In the interest of simplicity and economy, a transmitting station generates an encoded, control signal having a frequency which lies within the audio frequency band and which is decoded at a receiving station for reactivating the transducer. A means for decoding this remote control signal should be responsive to the encoded control signal which lies within the audio frequency band but should remain non-responsive to communication intelligence, to transmissions between other units, and to electrical noise. However, in many instances, communication apparatus of this type generate the same encoded remote control signal and it has been found that the signal of other users undesirably triggers the decoding circuit of a receiver being monitored. In other instances, certain frequency components of the intelligence being transmitted from a related transmitter or from an unrelated transmitter corresponds to the remote control signal frequency and undesirably confuse and activate the decoder circuit.
Various means have been provided including the use of reed filters, crystal filters and touch tone techniques for enhancing frequency discrimination of the decoder to the remote control system. However, these arrangements undesirably add substantial cost to the apparatus and are economically prohibitive for use with relatively low cost communication systems of the type described.
Accordingly, it is an object of this invention to provide an improved remote control for use with a communication system.
Another object of the invention is to provide an improved remote control with a communication system having an encoding signal lying within the same band of frequencies as the intelligence being communicated.
Another object of the invention is to provide a remote control for a communication system of the type described having improved means for providing a plurality of selectable encoding signals.
A further object of the invention is to provide a remote control for a communication system of the type described having an improved means for providing a plurality of encoding signals lying within a communication intelligence band and having means for tuning a decoder to the encoded signal.
Another object of the invention is to provide a remote control for a communication system of the type described, which exhibits improved discrimination and enhanced economy of construction.
Another object of the invention is to provide an improved remote control encoder for a communication system of the type described.
Another object of the invention is to provide an improved decoder for a communication system of the type described.
Another object of the invention is to provide encoder and decoder means which are adapted to be readily coupled to and decoupled from presently existing communication apparatus of the type described.